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Date:   Wed, 13 Dec 2023 17:05:13 +0000
From:   Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To:     Vishal Verma <vishal.l.verma@intel.com>
CC:     Dan Williams <dan.j.williams@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        <linux-kernel@vger.kernel.org>, <nvdimm@lists.linux.dev>,
        <linux-cxl@vger.kernel.org>, David Hildenbrand <david@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Huang Ying <ying.huang@intel.com>,
        Joao Martins <joao.m.martins@oracle.com>
Subject: Re: [PATCH v4 2/3] dax/bus: Introduce guard(device) for
 device_{lock,unlock} flows
Message-ID: <20231213170513.000036e8@Huawei.com>
In-Reply-To: <20231212-vv-dax_abi-v4-2-1351758f0c92@intel.com>
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        <20231212-vv-dax_abi-v4-2-1351758f0c92@intel.com>
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On Tue, 12 Dec 2023 12:08:31 -0700
Vishal Verma <vishal.l.verma@intel.com> wrote:

> Introduce a guard(device) macro to lock a 'struct device', and unlock it
> automatically when going out of scope using Scope Based Resource
> Management semantics. A lot of the sysfs attribute writes in
> drivers/dax/bus.c benefit from a cleanup using these, so change these
> where applicable.
> 
> Cc: Joao Martins <joao.m.martins@oracle.com>
> Suggested-by: Dan Williams <dan.j.williams@intel.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Hi Vishal,

I'm a big fan of this cleanup.h stuff so very happen to see this getting used here.
There are added opportunities for cleanup that result.

Note that almost every time I see people using this stuff they don't look again
at the code post the change so miss the wider cleanup that it enables. So you are
in good company ;)

Jonathan

> ---
>  include/linux/device.h |   2 +
>  drivers/dax/bus.c      | 109 +++++++++++++++++++------------------------------
>  2 files changed, 44 insertions(+), 67 deletions(-)
> 
> diff --git a/include/linux/device.h b/include/linux/device.h
> index d7a72a8749ea..a83efd9ae949 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -1131,6 +1131,8 @@ void set_secondary_fwnode(struct device *dev, struct fwnode_handle *fwnode);
>  void device_set_of_node_from_dev(struct device *dev, const struct device *dev2);
>  void device_set_node(struct device *dev, struct fwnode_handle *fwnode);
>  
> +DEFINE_GUARD(device, struct device *, device_lock(_T), device_unlock(_T))

Nice. I'd expect this to be widely adopted, so maybe to make things less painful
for backporting changes that depend on it, make this a separate trivial patch
rather than having this in here.

> +
>  static inline int dev_num_vf(struct device *dev)
>  {
>  	if (dev->bus && dev->bus->num_vf)
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 1ff1ab5fa105..ce1356ac6dc2 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -296,9 +296,8 @@ static ssize_t available_size_show(struct device *dev,
>  	struct dax_region *dax_region = dev_get_drvdata(dev);
>  	unsigned long long size;
>  
> -	device_lock(dev);
> +	guard(device)(dev);
>  	size = dax_region_avail_size(dax_region);
> -	device_unlock(dev);
>  
>  	return sprintf(buf, "%llu\n", size);
	return sprintf(buf, @%llu\n@, dax_region_avail_size(dax_region));
and drop the local variable that adds little perhaps?

>  }
> @@ -314,10 +313,9 @@ static ssize_t seed_show(struct device *dev,
>  	if (is_static(dax_region))
>  		return -EINVAL;
>  
> -	device_lock(dev);
> +	guard(device)(dev);
>  	seed = dax_region->seed;
>  	rc = sprintf(buf, "%s\n", seed ? dev_name(seed) : "");

return sprintf();

> -	device_unlock(dev);
>  
>  	return rc;
>  }
> @@ -333,10 +331,9 @@ static ssize_t create_show(struct device *dev,
>  	if (is_static(dax_region))
>  		return -EINVAL;
>  
> -	device_lock(dev);
> +	guard(device)(dev);
>  	youngest = dax_region->youngest;
>  	rc = sprintf(buf, "%s\n", youngest ? dev_name(youngest) : "");

return sprintf();

> -	device_unlock(dev);
>  
>  	return rc;
>  }
> @@ -345,7 +342,14 @@ static ssize_t create_store(struct device *dev, struct device_attribute *attr,
>  		const char *buf, size_t len)
>  {
>  	struct dax_region *dax_region = dev_get_drvdata(dev);
> +	struct dev_dax_data data = {
> +		.dax_region = dax_region,
> +		.size = 0,
> +		.id = -1,
> +		.memmap_on_memory = false,
> +	};
>  	unsigned long long avail;
> +	struct dev_dax *dev_dax;
>  	ssize_t rc;
>  	int val;
>  
> @@ -358,38 +362,26 @@ static ssize_t create_store(struct device *dev, struct device_attribute *attr,
>  	if (val != 1)
>  		return -EINVAL;
>  
> -	device_lock(dev);
> +	guard(device)(dev);
>  	avail = dax_region_avail_size(dax_region);
>  	if (avail == 0)
> -		rc = -ENOSPC;
> -	else {
> -		struct dev_dax_data data = {
> -			.dax_region = dax_region,
> -			.size = 0,
> -			.id = -1,
> -			.memmap_on_memory = false,
> -		};
> -		struct dev_dax *dev_dax = devm_create_dev_dax(&data);
> +		return -ENOSPC;
>  
> -		if (IS_ERR(dev_dax))
> -			rc = PTR_ERR(dev_dax);
> -		else {
> -			/*
> -			 * In support of crafting multiple new devices
> -			 * simultaneously multiple seeds can be created,
> -			 * but only the first one that has not been
> -			 * successfully bound is tracked as the region
> -			 * seed.
> -			 */
> -			if (!dax_region->seed)
> -				dax_region->seed = &dev_dax->dev;
> -			dax_region->youngest = &dev_dax->dev;
> -			rc = len;
> -		}
> -	}
> -	device_unlock(dev);
> +	dev_dax = devm_create_dev_dax(&data);
> +	if (IS_ERR(dev_dax))
> +		return PTR_ERR(dev_dax);
>  
> -	return rc;
> +	/*
> +	 * In support of crafting multiple new devices

rewrap this comment for the new indent.

> +	 * simultaneously multiple seeds can be created,
> +	 * but only the first one that has not been
> +	 * successfully bound is tracked as the region
> +	 * seed.
> +	 */
> +	if (!dax_region->seed)
> +		dax_region->seed = &dev_dax->dev;
> +	dax_region->youngest = &dev_dax->dev;

Trivial but blank line here would be a nice to have

> +	return len;
>  }


...

> @@ -1138,18 +1123,14 @@ static ssize_t mapping_store(struct device *dev, struct device_attribute *attr,
>  		return rc;
>  
>  	rc = -ENXIO;

Not needed with suggested changes that follow.

> -	device_lock(dax_region->dev);
> -	if (!dax_region->dev->driver) {
> -		device_unlock(dax_region->dev);
> +	guard(device)(dax_region->dev);
> +	if (!dax_region->dev->driver)
>  		return rc;
		return -ENXIO;
> -	}
> -	device_lock(dev);
>  
> +	guard(device)(dev);
>  	to_alloc = range_len(&r);
>  	if (alloc_is_aligned(dev_dax, to_alloc))
>  		rc = alloc_dev_dax_range(dev_dax, r.start, to_alloc);
Flip logic here and I'd drop the ternary stuff as well - same in other
similar cases in this patch (though that is just personal taste)

	if (!alloc_is_aligned(dev_dax, to_allco))
		return -ENXIO.

	rc = alloc_dev_dax_range(dev_dax, r.start, to_allco)
	if (rc)
		return rc;

	return len;

> -	device_unlock(dev);
> -	device_unlock(dax_region->dev);
>  
>  	return rc == 0 ? len : rc;
>  }

>